Method and apparatus for frequency selective beam forming

RELATED APPLICATION(S)

This application is a continuation of U.S. application Ser. No. 10/234,036, filed Aug. 30, 2002, now U.S. Pat. No. 6,788,268 which is a continuation-in-part of U.S. application Ser. No. 09/879,807, filed Jun. 12, 2001, now U.S. Pat. No. 6,448,938. The entire teachings of the above applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

In the area of wireless communications, time division multiple access (TDMA) and code division multiple access (CDMA) protocols are used for communicating from a base station to a mobile station. The TDMA technology uses a single frequency for transmitting and receiving signals, while the CDMA systems use one frequency band for transmitting signals and another frequency band for receiving signals. In both cases, multipath can be a source of interference.

<figref idref="DRAWINGS">FIG. 1</figref> is an example environment <b>100</b> in which multipath is typically present. The environment <b>100</b> includes a first antenna tower <b>105</b><i>a </i>and a second antenna tower <b>105</b><i>b</i>. Each antenna tower <b>105</b><i>a</i>, <b>105</b><i>b </i>has an associated base station (not shown). The environment <b>100</b> further includes a first office building <b>110</b><i>a </i>and a second office building <b>110</b><i>b</i>. In the first office building <b>110</b><i>a</i>, a subscriber unit <b>115</b> is within range of signals from both antenna towers <b>105</b><i>a</i>, <b>105</b><i>b. </i>

There are several signaling paths from the antenna towers <b>105</b><i>a</i>, <b>105</b><i>b </i>to the subscriber unit <b>115</b>. A first signaling path <b>120</b> is a direct signaling path from the first antenna tower <b>105</b><i>a </i>to the subscriber unit <b>115</b>. A second signaling path <b>125</b> includes a reflection off the second office building <b>110</b><i>b </i>as the respective signal travels from the first antenna tower <b>105</b><i>a </i>to the subscriber unit <b>115</b>. A third signaling path <b>130</b> is a direct signaling path from the second antenna tower <b>105</b><i>b </i>to the subscriber unit <b>115</b>.

The first signaling path <b>120</b> is in the direction of the first antenna tower <b>105</b><i>a</i>. The subscriber unit <b>115</b> does not know where the first antenna tower <b>105</b><i>a </i>is located. The subscriber unit <b>115</b> can only point (i.e., direct a beam) in the direction of the strongest desired signal, if the subscriber signal is equipped with a steering antenna. The strongest desired signal is in the direction between the locations of the first antenna tower <b>105</b><i>a </i>and second office building <b>110</b><i>b. </i>

In direction finding (DF), multipath tends to be harmful because it masks the true direction of the signal. The component of the multipath that is in-phase with the first signaling path <b>120</b> is actually helpful, and thus, the direction change is inconsequential. So, multipath is not all interference. However, the third signaling path <b>130</b> is all interference because it is not the same signal as being transmitted on the first signaling path and can never be in-phase with the signal on the first signaling path.

If the subscriber unit <b>115</b> employs a phased array antenna, it can use the phased array antenna to steer an associated antenna beam toward the first antenna tower <b>105</b><i>a</i>, or, in the case of multipath as just described, in the direction of the strongest desired signal. Additionally, the phased array antenna may be used to steer the associated antenna beam to receive signals from only the direct signaling path <b>120</b> from the first antenna tower <b>105</b><i>a </i>to remove the multipath effects (i.e., signal fading) caused by the second signal <b>125</b> or interference caused by the third signaling path <b>130</b>.

<figref idref="DRAWINGS">FIG. 2</figref> is a block diagram of the phased array antenna used by the subscriber unit <b>115</b> of <figref idref="DRAWINGS">FIG. 1</figref> capable of steering the associated beam, where the steering is done by phase shifting the RF signals to/from the antenna elements composing the array antenna <b>200</b>. The phased array antenna <b>200</b> is composed of antenna sub-assemblies <b>205</b>. Each antenna sub-assembly <b>205</b> includes an antenna element <b>210</b>, duplexer <b>215</b>, and phase shifter <b>220</b>. A control signal <b>225</b> is used to adjust the phase shifts imposed by each of the phase shifters <b>220</b>.

In transmission mode, the sub-assemblies <b>205</b> of phased array antenna <b>200</b> receives a signal <b>230</b>. The signal is phase shifted by the phase shifters <b>220</b> in a manner where, when the beams of all the antenna elements <b>210</b> are combined, the resulting effective beam (not shown) is directed as defined by the control signals <b>225</b>. The signal <b>230</b> passes from the phase shifters <b>220</b> to the antenna elements <b>210</b> via the duplexes <b>215</b>, which are in a transmit mode.

In receive mode, the antenna elements <b>210</b> receive RF signals most strongly from a direction defined by the same control signals <b>225</b>. The antenna elements <b>210</b> provide the received signals to the duplexes <b>215</b>, which are set in a receive mode to allow the received RF signal to pass to the phase shifters <b>220</b>. The phase shifters <b>220</b> provide signals <b>230</b>, which have been phase shifted, to a summer (not shown) to reconstruct the signal. The reconstructed signal is thereafter processed by a receiver (not shown).

SUMMARY OF THE INVENTION

Recently, experiments to determine optimal gain between a subscriber unit and antenna tower have shown that, when using transmission signals of different frequencies, the optimum signaling direction varies for the different frequencies. In CDMA technology, as defined for a subscriber unit, the receive (RX) signals range between 1930–1990 MHz, and the transmission (TX) signals span from 1850–1910 MHz. Further tests were conducted to determine whether the optimum signaling paths differ for the TX and RX signals of the CDMA technology, as in the case of transmitting signals having different frequencies. These further experiments proved that, in fact, the optimum signaling paths between a subscriber unit and base station antenna tower are frequency dependent, affecting signaling paths of TX and RX signals.

At least one reason for different optimum signaling directions for signals at different frequencies has been determined to be caused by different angles of refraction as the signals travel between the antenna tower and the subscriber unit antenna. For example, in CDMA technology, when the TX and RX signals travel through a glass of an office building window, the TX signals “bend” at a first angle and the RX signals “bend” at a second angle. The different angles of refraction may also result in the signals taking multiple paths inside an office in which the subscriber unit resides. Further, the TX and RX signals bend around objects external from the office building at different angles, which can be another source of difference in transmission paths. The net result of differences in angles and multipath is at best a reduction in signal-to-noise ratio (SNR) and at worst an interference causing disruption in communication.

In directional antenna technology, there is an assumption that the optimum directions of the signals traveling in the forward and reverse links are along the same path. Thus, once a direction has been selected, typically based on RX signal-to-noise ratio (SNR), the selected direction is used for both TX and RX signals. While the selected direction may have been found to be optimal for one of the links, the selected direction of the antenna directivity may be sub-optimal for the other link, as learned during the experiments discussed above.

In general, the present invention provides a subscriber unit with an ability to transmit and receive signals in different directions simultaneously to allow for optimum gain in both directions. In this way, refraction and multipath effects resulting from communication signals operating at different frequencies can be compensated for to improve gain in both the forward and reverse links.

Accordingly, one embodiment of the present invention includes a directive antenna having plural antenna elements arranged in an antenna array. Frequency selective components are coupled to respective antenna elements, where the frequency selective components provide simultaneous frequency discrimination. At least two weighting structures are coupled to the frequency selective components to produce independently steerable beams having spectrally separated signals.

In an alternative embodiment, the present invention includes a directive antenna having plural antenna elements arranged in a parasitic antenna array. Frequency selective components are connected to a first subset of the antenna elements. Weighting structures are connected to a second subset of the antenna elements. The first and second subsets of antenna elements may be connected by a space-fed power distribution system to produce independently steerable beams having spectrally separated signals.

In another alternative embodiment, the present invention includes a directive antenna having plural antenna elements arranged in a parasitic antenna array. Frequency selective components are connected to an active antenna element. Weighting structures are connected to passive antenna elements positioned substantially equidistant from the active antenna element. The active and passive antenna elements are connected by a space-fed power distribution system to produce independently steerable beams having spectrally separated signals.

The frequency selective components may be designed to transmit and receive signals in, for example, a CDMA system in which the transmit and receive signaling bands are separated. The frequency selective components may also be designed to separate same direction signals having different frequencies. The frequency selective components may also separate more than two signals, in which case more than two phase-shifting elements are coupled to the frequency selective components. The frequency selective components may include a printed or non-printed technology, or combination thereof.

The weighting structures may include phase shifting elements to steer the beams independently. Independent control signals set-up respective phase shifts. The weighting structures may further include at least one variable gain amplifying component to independently amplify the signals received by or transmitted by the respective antenna elements. By having more than one variable gain amplifying component associated with each antenna element, the respective shapes of the beams can be optimized.

The directive antenna may further include a combiner associated with each beam being produced to combine signals transmitted or received by the antenna elements.

By having independently steerable and shapable beams, the directive antenna is attractive for use in a multi-band and/or multipath environment.

In one embodiment, the subscriber unit optimizes a forward link beam pattern (i.e., a receive, RX, beam to receive signals in the forward link) based on a received pilot signal from a base station. The subscriber unit may also optimize the reverse (i.e., transmit, TX) beam pattern based on a signal quality of a given received signal via a feedback metric from a base station over the forward link. Further, at the same time, the subscriber unit may steer the reverse beam (TX beam) in the direction of maximum received power of a signal from a given base station, while optimizing the forward beam (RX beam) on a best signal-to-noise ratio (SNR) or carrier-to-interference (C/I) level. These and other techniques for determining the direction of the beams in both forward and reverse links (i.e., receive and transmit beams, respectively, from the point of view of the subscriber unit) are provided in U.S. patent application Ser. No. 09/776,396 filed Feb. 2, 2001, entitled “Method and Apparatus for Performing Directional Re-Scan of an Adaptive Antenna,” by Proctor et al, the entire teachings of which are incorporated herein by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

<figref idref="DRAWINGS">FIG. 1</figref> is a diagram of an environment in which a wireless communication system is deployed;

<figref idref="DRAWINGS">FIG. 2</figref> is a block diagram of a prior art phased array antenna system;

<figref idref="DRAWINGS">FIG. 3</figref> is a diagram of an environment in which a system employing the principles of the present invention is operating;

<figref idref="DRAWINGS">FIG. 4</figref> is a block diagram of a dual independent beam array used by the system of <figref idref="DRAWINGS">FIG. 3</figref>;

<figref idref="DRAWINGS">FIG. 5</figref> is a detailed schematic diagram of an embodiment of the dual independent beam array of <figref idref="DRAWINGS">FIG. 4</figref>;

<figref idref="DRAWINGS">FIG. 6</figref> is a schematic diagram of an embodiment of a frequency selective component used in the dual independent beam array of <figref idref="DRAWINGS">FIG. 5</figref>;

<figref idref="DRAWINGS">FIG. 7</figref> is a frequency response plot of a typical frequency selective component shown in <figref idref="DRAWINGS">FIG. 6</figref>;

<figref idref="DRAWINGS">FIG. 8</figref> is a flow diagram of an embodiment of a process employed by the system of <figref idref="DRAWINGS">FIG. 3</figref>;

<figref idref="DRAWINGS">FIG. 9</figref> is a schematic diagram of the dual independent beam array of <figref idref="DRAWINGS">FIG. 4</figref> having annotations of process steps;

<figref idref="DRAWINGS">FIG. 10</figref> is a schematic diagram of an alternative embodiment of the dual independent beam array of <figref idref="DRAWINGS">FIG. 9</figref> having a parasitic antenna array and annotations of the same process steps;

<figref idref="DRAWINGS">FIG. 11</figref> is a schematic diagram of an example of weighting structures connected to antenna elements in the parasitic antenna array of <figref idref="DRAWINGS">FIG. 10</figref>;

<figref idref="DRAWINGS">FIG. 12</figref> is a schematic diagram of an example of a particular weighting structure of <figref idref="DRAWINGS">FIG. 11</figref>; and

<figref idref="DRAWINGS">FIG. 13</figref> is a block diagram of an alternative layout of the parasitic array of <figref idref="DRAWINGS">FIG. 10</figref>.

DETAILED DESCRIPTION OF THE INVENTION

A description of preferred embodiments of the invention follows.

<figref idref="DRAWINGS">FIG. 3</figref> is a diagram illustrating an example usage of the present invention. A portable personal computer <b>305</b> is coupled via an antenna cable <b>310</b> to an antenna array <b>315</b>. The antenna array <b>315</b> is capable of forming a directive beam due to the spacing of the antenna elements <b>317</b>.

As shown, the antenna array <b>315</b> provides two beams: a transmit beam <b>320</b> and a receive beam <b>325</b>. The transmit beam <b>320</b> is directionally pointed to transmit a signal <b>120</b> through a window <b>330</b> to an antenna tower <b>105</b><i>a </i>in an optimal direction. Similarly, the receive beam <b>325</b> is directionally pointed to receive a receive beam <b>125</b> from the antenna tower <b>105</b><i>a </i>through the window <b>330</b> in an optimal direction.

In the case of CDMA for a subscriber unit, transmit (TX) signals operate at 1850–1910 MHZ and receive (RX) signals operate between 1930–1990 MHZ. The difference in frequencies between these two signals is enough to cause, for example, a difference in the angle of refraction of the signals transmitting through the window <b>330</b>, among other directional differences. To optimize the signal-to-noise ratio and mitigate the effects of multipath and other signal interferences, the antenna array is capable of providing the TX and RX beams simultaneously, while using the same antenna array <b>315</b>.

To optimize the receive beam angle, the system controlling the receive beam angle may use the signal-to-noise ratio (SNR) of received signals as a parameter for determining the best angle of the receive beam. A method that may be used to optimize the receiving look angle is described in U.S. Pat. No. 6,100,843 and related pending U.S. patent application Ser. No. 09/616,588, filed Jul. 14, 2000, entitled “Adaptive Antenna for Use in Same Frequency Network,” by Proctor et al.; the entire teachings of both are incorporated herein by reference.

To optimize the transmit beam angle, the system controlling the transmit beam angle transmits a signal at different angles and allows the base station (not shown) at the tower <b>105</b><i>a </i>to feed back whether the signaling direction is optimal. Various implementations of transmitting and feeding back signals to determine the optimum transmit beam angle can be employed, such as those described in U.S. patent application Ser. No. 09/776,396 filed Feb. 2, 2001, entitled “Method and Apparatus for Performing Directional Re-Scan of an Adaptive Antenna,” by Proctor et al., the entire teachings of which are incorporated herein by reference.

For example, as described in U.S. patent application Ser. No. 09/776,396, the subscriber unit may optimize the forward link beam pattern (i.e., RX beam) based on how well the subscriber unit receives a pilot signal. The subscriber unit may optimize its reverse link beam (i.e., TX beam) pattern based on a received signal quality of a given signal via a feedback metric from a given base station over the forward link. Further, the subscriber unit may steer the reverse link beam in the direction of maximum received power of a signal from a base station, while optimizing the forward beam (i.e., RX beam) on a best signal-to-noise ratio (SNR) or carrier-to-interference (C/I) level.

The principles of the present invention are useful in systems in which signals of different frequencies are used. For example, besides a system having transmit and receive beams having different frequencies, the system may be used to transmit two signals at two different frequencies. Further, a receive signal and two spectrally separated transmission signals can be used, where three different beam angles can be provided by the antenna array <b>315</b> corresponding to the three signals. The number of simultaneous beam angles requires a corresponding number of phase shifters and frequency selective components providing the same number of frequency channels.

<figref idref="DRAWINGS">FIG. 4</figref> is a block diagram of a system used to provide the transmit beam <b>320</b> and receive beam <b>325</b>. An antenna assembly <b>405</b> includes an antenna element <b>210</b>, frequency selective component <b>410</b>, receive weighting structure <b>415</b>, (e.g., phase shifter and amplifier and transmit weighting structure <b>420</b>.

The weighting structures <b>415</b>, <b>420</b> are controlled by respective control signals <b>425</b>, <b>435</b>. The receive weighting structure <b>415</b> supports a receive signal <b>430</b>, and the transmit weighting structure <b>420</b> supports a transmit signal <b>440</b>.

The antenna assembly <b>405</b> is one of n number of antenna assemblies <b>405</b> that compose the antenna array <b>315</b> (<figref idref="DRAWINGS">FIG. 3</figref>). The number of weighting structures <b>415</b>, <b>420</b> in each antenna assembly <b>405</b> determines the number of beams that may be simultaneously generated at different angles and/or patterns by the antenna array <b>315</b>. The frequency selective component <b>410</b> provides discrimination between signals at different frequencies. Preferably, the frequency selective component <b>410</b> provides passive means for splitting the signals at different frequencies, so as to minimize the power required by the antenna assembly <b>405</b>.

Independent control of the weighting structures <b>415</b>, <b>420</b> is provided by the controller <b>445</b>, which generates the receive control signals <b>425</b> and transmit control signals <b>435</b>. The controller <b>445</b> may include the intelligence to provide the angle and/or pattern for the transmit beam <b>320</b> and receive beam <b>325</b> (<figref idref="DRAWINGS">FIG. 3</figref>), or, a local system (e.g. portable computer <b>305</b>) may provide the intelligence for determining the optimum angles and/or patterns of the beams. In such an embodiment, the local system then provides the controller <b>445</b> with the optimum angle and/or pattern information, which, in turn is provided to the weighting structures <b>415</b>, <b>420</b>.

<figref idref="DRAWINGS">FIG. 5</figref> is a schematic diagram of a more extensive embodiment of the dual independent beam array system of <figref idref="DRAWINGS">FIG. 4</figref>. According to the principles of the present invention, both a transmit beam <b>320</b> and receive beam <b>325</b> can be independently and simultaneously directed by the same antenna array <b>315</b> (<figref idref="DRAWINGS">FIG. 3</figref>).

The dual independent beam array system <b>500</b> includes plural transmit/receive beam forming networks <b>505</b>. Each network <b>505</b> includes an antenna element <b>510</b>, frequency selective component <b>515</b>, and receive and transmit weighting structures <b>415</b>, <b>420</b>, respectively. In this embodiment, the receive weighting structures <b>415</b> include a receive variable-gain, low-noise amplifier <b>520</b> and a receive phase shifter <b>522</b>. The transmit weighting structures <b>420</b> include a transmit, variable-gain, low-noise amplifier <b>525</b>.

The amplifiers <b>520</b>, <b>525</b> in the networks <b>505</b> provide better performance at possibly higher expense than having single receive and transmit amplifiers located farther from the antenna elements <b>510</b>. However, since the beams are directive, having higher gain in the peak beam direction, the amplifiers <b>520</b>, <b>525</b> do not necessarily need to be high power, as might be in the case of an omni-directional antenna, so the per-amplifier cost may be relatively inexpensive.

Alternatively, the low noise amplifiers <b>520</b> and power amplifiers <b>525</b> could be behind the combiner <b>530</b> and <b>535</b>. The system <b>500</b> may be less expensive due to a single amplifier implementation, but would likely have worse performance than the distributed amplifier embodiment shown.

The phase shifters <b>522</b>, <b>527</b> can be generic phase shifters or of the type described in U.S. patent application Ser. No. 09/774,534 filed Jan. 31, 2001, entitled “Electronic Phase Shifter With Enhanced Phase Shift Performance” by Chiang et al., the entire teachings of which are incorporated herein by reference.

A first combiner <b>530</b> transmits signals to the N transmit portions of the beam forming networks <b>505</b>. A second combiner <b>535</b> receives signals from the N receive portions of the beam forming networks <b>505</b>. The combiner may be a typical combiner, such as a Wilkinson power combiner.

Further, the antenna elements <b>510</b> may be generic antenna elements capable of being used in an antenna array for beam forming other antenna type, such as antennae shown and described in U.S. patent application Ser. No. 09/773,277, filed Jan. 31, 2001, entitled “Stacked Dipole Antenna for Use in Wireless Communications Systems”, by Chiang et al. and U.S. patent application Ser. No. 09/773,377, filed Jan. 31, 2001, entitled “Printed Circuit Low Profile Vertical Dipole”, by Gothard et al., the entire teachings of both are incorporated herein by reference.

Further, the frequency selective components <b>515</b> may be of several types, including printable and/or non-printed types. It is important for the frequency selective components <b>515</b>, however, to provide sufficient frequency-band isolation so as not to leak TX and RX signals onto each other, thereby creating signal noise.

An example of a printed frequency selective component is provided in <figref idref="DRAWINGS">FIG. 6</figref>. Referring to <figref idref="DRAWINGS">FIG. 6</figref>, the frequency selective component <b>315</b> includes two 90 degree hybrids <b>605</b>, two low-pass filters (LPF) <b>610</b>, and one 180 degree, fixed value, phase shifter <b>615</b>. The signal received from the antenna element <b>150</b> is directed to a first 90 degree hybrid <b>605</b> and output to a low noise amplifier (LNA) <b>320</b><i>a</i>. The amplified received signal is provided to a receiver (not shown) for further processing.

A transmitter (not shown) provides a signal to the power amplifier (PA) <b>320</b><i>b</i>. The amplified transmit signal is processed by the frequency selective component <b>315</b> and provided to the antenna element <b>510</b> (not shown). The signal being transmitted by the antenna is preferably isolated by the frequency selective component <b>315</b> from the low noise amplifier <b>320</b><i>a. </i>

The frequency selective component <b>315</b> is low in cost, but may not provide the same level of performance as other possible frequency selective components. For example, the frequency selective component <b>315</b> does not provide a high degree of isolation between the transmit and receive signals within 80 MHz of each other because of its low Q characteristic. However, because the frequency selective component is printable, it is small and inexpensive to make.

An example of alternative frequency selective component is commercially available from Agilent® Technologies, which is referred to as a thin-film bulk acoustic resonator (FBAR), which provides a high-Q filter in a small package profile. An HPMD-7903, is an example of such an FBAR duplexed and is relatively small. The HPMD-7903 has good performance characteristics, but is more expensive than the printable frequency selective component of <figref idref="DRAWINGS">FIG. 6</figref>.

Yet another alternative embodiment of the frequency selective component <b>315</b> is a ceramic duplexer. A ceramic duplexer (i) has a high performance, high-Q filter characteristic, (ii) is relatively cheap, but (iii) is relatively large. Other performance characteristics to consider when selecting a frequency selective component include insertion loss, noise blocking, power handling, transmit and receive bandwidths, isolation between channels, in-band ripple, impedance, and temperature characteristics.

<figref idref="DRAWINGS">FIG. 7</figref> is an exemplary frequency response plot <b>700</b> of a frequency selective component <b>315</b>. The frequency response plot <b>700</b> indicates the pass-band regions of the receive pass band <b>705</b><i>a </i>and the transmit pass band <b>705</b><i>b</i>. The transmit and receive characteristics are for a subscriber unit in a CDMA system, in which the transmit band is specified between 1850–1910 MHZ and the receive band is specified between 1930–1990 MHZ.

<figref idref="DRAWINGS">FIG. 8</figref> is a flow diagram of an embodiment of a process <b>800</b> employed by the dual independent beam array system <b>500</b> (<figref idref="DRAWINGS">FIG. 5</figref>). The process <b>800</b> begins in step <b>805</b>. In step <b>810</b>, the process <b>800</b> determines whether a control signal has been received to adjust the direction of the antenna array receive beam. If yes, then in step <b>815</b>, the process <b>800</b> controls the state of receive weighting structures <b>415</b> (<figref idref="DRAWINGS">FIG. 5</figref>) coupled to an antenna array. If no, then the process <b>800</b> continues in step <b>820</b>.

In step <b>820</b>, the process <b>800</b> determines whether a control signal has been received to adjust the transmit beam direction. If yes, then the process <b>800</b> continues in step <b>825</b>, in which the process <b>800</b> controls the state of the transmit weighting structures <b>420</b> (<figref idref="DRAWINGS">FIG. 5</figref>) coupled to the same antenna array. The process <b>800</b> continues in step <b>810</b>, unless or until the system is shut off.

Alternative embodiments of the process <b>800</b> may include other steps or other decision points to control the antenna array <b>315</b> (<figref idref="DRAWINGS">FIG. 3</figref>) (i) in a manner as discussed above, such as controlling the amplifiers <b>520</b>, <b>525</b> (<figref idref="DRAWINGS">FIG. 5</figref>), or (ii) in a manner not described but commonly understood in the art for directive beam control.

The process <b>800</b> may be executed by the controller <b>445</b> (<figref idref="DRAWINGS">FIG. 4</figref>) or a master controller, such as a controller in the personal computer <b>305</b> (<figref idref="DRAWINGS">FIG. 3</figref>).

The above description describes an all-active array for providing a dual beam formation for use by portable access terminals and other wireless devices. The following description provides teachings for an alternative embodiment that includes passive antenna elements parasitically coupled to at least one active antenna element. Before discussing this alternative embodiment, a brief review of the first embodiment is provided with four steps of a process performed therein being highlighted.

<figref idref="DRAWINGS">FIG. 9</figref> is a generalized schematic diagram of the all-active antenna array embodiment of <figref idref="DRAWINGS">FIG. 4</figref>, in which the antenna assembly <b>405</b> may use two power dividers <b>530</b>, <b>535</b>, multiple diplexers <b>515</b>, multiple phase shifters <b>522</b>, <b>527</b>, and multiple amplifiers <b>520</b>, <b>525</b> to create two independently steered beams <b>320</b>, <b>325</b>.

Tracing the path of the network, the Tx signal goes through the power divider <b>530</b> (Step A), where the signal is divided N ways, where N is the number of antenna elements <b>317</b> in the antenna array <b>315</b>. The signal in each way goes through S<b>12</b> of the phase shifter <b>527</b> (Step B) and amplifier <b>525</b>, and then meets up with an equivalent way of the Rx signal. The two ways, Tx and Rx, then go through the diplexer <b>515</b> (Step C) to have the two paths combined into one. That one path then connects to one of the N antenna elements <b>317</b> and radiates (Step D). Together with other antenna elements <b>317</b>, two separate beams <b>320</b>, <b>325</b> are formed, each corresponding to a different band, because the phase of each band is separately controlled by the phase shifters <b>527</b>, <b>522</b> before they are combined.

<figref idref="DRAWINGS">FIG. 10</figref> is a schematic diagram of a second embodiment of a directive antenna to produce independently steerable beams having spectrally separated signals. The power dividers <b>530</b>, <b>535</b> of the previous embodiment (<figref idref="DRAWINGS">FIG. 9</figref>) can be replaced by a space fed power distribution system <b>1015</b>. The use of a single diplexer <b>515</b> rather than multiple diplexers may be used. The phase shifters <b>527</b>, <b>522</b> in the T/R beam forming modules <b>405</b> of <figref idref="DRAWINGS">FIG. 9</figref> may be replaced by frequency selective impedances <b>1010</b>, S<b>11</b>s. The diplexers <b>515</b> use filters <b>610</b> (<figref idref="DRAWINGS">FIG. 6</figref>) to separate the two bands. Filters are microwave devices that have special S<b>12</b> frequency characteristics. In this second embodiment, it is suggested that frequency selective impedances <b>1010</b> having equivalent S<b>11</b> frequency characteristics as the filters <b>610</b> can be used instead.

This second embodiment of the directive antenna depicted in <figref idref="DRAWINGS">FIG. 10</figref> has a similar path as the first embodiment of <figref idref="DRAWINGS">FIG. 9</figref>, but has a different order of the steps taken. The Tx signal path combines with the Rx path, through the help of a diplexer <b>515</b> (Step C), and forms a single path. The single path then leads to a power divider, which has been changed to a space fed power divider <b>1015</b> (Step A). One of the N-way divided powers enters a passive element <b>1005</b> and sees the S<b>11</b> of a frequency selective impedance <b>1010</b> (Step B), which may be a switched load, also referred to as a weighting structure. The load sends the signal back out of the passive element <b>1005</b> (Step D) with its phase, and also amplitude if so desired, altered or controlled by the load selected. The reradiated waves from all the passive elements <b>1005</b> form a beam. To form two beams through frequency selectivity, the frequency selective impedances <b>1010</b> are frequency selective.

Referring now to <figref idref="DRAWINGS">FIG. 11</figref>, the frequency selective process is provided by a properly designed frequency selective impedance <b>1010</b>, interchangeably referred to hereafter as S<b>11</b>. The S<b>11</b> can be the result of seeing a short circuit (SC) <b>1110</b> or open circuit (OC) <b>1115</b>. Ideally, the short circuit <b>1110</b> and open circuit <b>1115</b> have unity amplitudes and only the phases vary from being either 0 or 180 degrees. A possible switching arrangement using a mechanical, electrical, or electromechanical switch <b>1105</b> is shown in <figref idref="DRAWINGS">FIG. 11</figref>.

The S<b>11</b> can also see impedances Z<b>1</b><b>1120</b> or Z<b>2</b><b>1125</b>, which have impedance characteristics as a function of frequency. Z<b>2</b><b>1125</b> returns 0 phase for Tx and 180 for Rx. Z<b>1</b><b>1120</b> does the opposite. In <figref idref="DRAWINGS">FIG. 11</figref>, the reradiated phases could take one of the four combinations: 1) Tx and Rx have 0 phase, 2) Tx and Rx both have 180 degrees phase, 3) Tx has 0 and Rx has 180 degrees phases, and 4) Tx has 180 and Rx 0 degree phases. Each element <b>1110</b>, <b>1115</b>, <b>1120</b>, <b>1125</b> is in one of the 4 states. Together, they form two sets of phase distributions, thus two different beams <b>320</b>, <b>325</b>, each corresponding to a different frequency band represented by phase diagrams <b>1122</b>, <b>1127</b>. There can be more variations to the design such as non-zero or 180 degree phase shifters (e.g., 30, 60, or 90 degrees phase shifters). There can also be more switch positions to increase phase steps and phase combinations.

<figref idref="DRAWINGS">FIG. 12</figref> is a schematic providing an example of how to generate Z<b>1</b>(<i>f</i>) <b>1120</b> and Z<b>2</b>(<i>f</i>) <b>1125</b>. In this example, a simple LC series combination of an inductor <b>1205</b> and a capacitor <b>1210</b> is given. The magnitude and phase of the impedance are plotted <b>1215</b>, <b>1220</b> as a function of frequency, showing low magnitude at resonance with an abrupt change in phase. The phase plot <b>1220</b> is “S” shaped, so it can be used for Z<b>2</b>(<i>f</i>) <b>1125</b>. A complement of that circuit can be used for Z<b>1</b>(<i>f</i>) <b>1120</b>. Sharp cutoff can come from adding more poles, and broad bands can come from stagger tuning. See George R. Matthaei, et al., Microwave Filters, Impedance-Matching, Networks and Coupling Structures, (NY: McGraw-Hill, 1964), which discusses some synthesis techniques for microwave impedance-matching circuits. Switching can be incorporated into the impedance circuit itself to provide fine increments of reflected phase. Electronics can also be used to make continuous phase variations rather than discrete phase variations.

When this concept is applied to a circular array, as shown in <figref idref="DRAWINGS">FIG. 13</figref>, the result is that the dual beams <b>320</b>, <b>325</b> can independently scan, covering 360 degrees in the array plane. An application, such as one provided in U.S. Pat. No. 6,369,770, entitled “Closely Spaced Antenna Array,” by Griff Gothard, et al., can thus be made to support dual beams. The concept can also extend to multiple frequencies, beyond two, to cover multiple band applications.

While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.